Evolutionary consequences of a catadromous life-strategy on the genetic structure of European eel (Anguilla anguilla L.)
Maes, G.E. (2005). Evolutionary consequences of a catadromous life-strategy on the genetic structure of European eel (Anguilla anguilla L.). PhD Thesis. Katholieke Universiteit Leuven. Faculteit Wetenschappen: Leuven. 223 pp.
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| Keywords |
Biology > Genetics
Anguilla anguilla (Linnaeus, 1758) [WoRMS]
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| Abstract |
Marine organisms usually exhibit a high genetic diversity, a subtle population structure and a low level of genetic differentiation, compared to freshwater organisms. The subtle genetic differences in time and space reflect the continuity of the marine environment. Marine organisms experience a wide range of intrinsic and extrinsic influences during their life cycle, which considerably impact their biological population size and genetic population structure. Furthermore, genetic variability is crucial for the survival of organisms as it enables evolution while maintaining fitness. Marine species however have a high genetic load, affecting the population even more during a population decline or bottleneck. The European eel Anguilla anguilla (Anguillidae; Teleostei), although inhabiting fresh- and saltwater, represents no exception. Its spawning habitat in the Sargasso Sea and extensive migrations across the North Atlantic Ocean qualify it fully as a marine species. This thesis describes the multiple evolutionary consequences of the catadromous life-strategy on the genetic structure of the European eel.Recent data based on microsatellite markers show a subtle genetic structure in the European eel following an Isolation-by-Distance (IBD) pattern. But since genetic introgression from the American eel into the European eel has been suggested in the North Atlantic Ocean, reliable tests were developed to define the species status of the European eel. In this first part the interspecific conservation of a set of microsatellites was tested on other Anguilla taxa and the power of species discrimination was assessed. We then applied this knowledge by screening Icelandic and European samples for introgression of American eel. Indications of unequal but restricted hybridisation were detected, likely maintained through selection against hybrids and the preservation of migrational cues.In the second part, the genetic variability and differentiation between various glass and silver eel populations was compared over a broad geographical range (Iceland to Morocco; Spain to Turkey) with temporal replications. In the first instance a pattern of Isolation-by- Distance was detected in adult populations using allozyme markers. Following a more extended geographical sampling, the temporal stability of this pattern could not be confirmed; the temporal differentiation between populations clearly exceeded the geographical component. By sampling recruiting glass eels over a three-year period, a stronger genetic differentiation was found between temporally separated cohorts. Inter-annual differentiation was much higher than the geographical differentiation. The population genetic structure of eel is likely determined by a double process: (I) a large scale pattern of Isolation-by-Time (IBT) among spawning cohorts, and (2) a smaller scale variance in adult reproductive success (genetic patchiness) among seasonally separated cohorts, most likely originating from oceanic and climatic influences.In the third part, the relation between multi-locus heterozygosity (MLH) and fitness components was studied. If an association exists between genetic variability and fitness traits, it is even more important to maintain the population size of European eel. The catastrophic decline of the European eel might be the consequence of an accelerated loss of genetic diversity, with extinction as possible outcome. This hypothesis was tested in a polluted natural environment and in an eel farm. Eel from three Belgian drainage basins were screened for fitness, heavy metal bioaccumulation and genetic variation. There was a strong negative correlation between MLH and bioaccumulation in highly polluted eels. In a second study, aquacultured eel were screened for fitness and genetic variation; MLH was correlated to growth rate. In both studies, this effect was mainly attributed to metabolical enzymes important in the energy cycle, which points to the importance of |
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- Population structure and dispersal of Anguilla anguilla (European Eel), more
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